Trialkoxysilanes undergo various reactions such as addition, co-polymerization, co-polycondensation and disproportionation with other organic compounds to form organosilicon compounds.
The disproportionation reaction leads to formation of silane, which is a precursor for solar-grade silicon production. The widely used method for the synthesis of alkoxysilanes involves the reaction of silicon with hydrochloric acid to form trichlorosilane (Equation 1) which is then reacted with primary alcohols in the presence of a copper catalyst (Equation 2).Si+3HCl→SiHCl3+H2  (1)SiHCl3+3ROH→SiH(OR)3+3HCl  (2)
However, this approach is faced with challenges including the poor conversion of silicon, low selectivity and poor yield of the desired trialkoxysilane product in addition to the toxic and corrosive hydrochloric acid by-product.
Therefore, much attention has been paid to the development of a direct synthesis method (Equation 3), and the improvement of the selectivity for the trialkoxysilane.Si+3ROH→SiH(OR)3+H2  (3)
The direct synthesis method has to date been carried out in continuously stirred slurry phase tank reactors using heat transfer solvents, such as diphenylalkanes. The use of heat transfer solvents result in prolonged catalyst activation time and also complicate the purification process. This slurry phase method also suffers from low selectivity and yield of the desired trialkoxysilane product, as well as the slow conversion of metallic silicon.
JP2001-178018 describes a production process for polycrystalline silicon and high purity silicon. However, the method described for the production of trialkoxysilane takes place in a fluidized bed reactor, and according to the examples provided, in the presence of a catalyst containing Cu, Al, and Fe. According to the description the method achieves selectivity for trimethoxysilane of about 75%. Such a low selectivity for the desired product may be problematic for a number of reasons, including the associated negative cost implication, and the need for additional separation steps in the process.
Accordingly there is a need for an alternative method for the synthesis of trialkoxysilanes that addresses the above-mentioned shortcomings.